The present invention relates to a gripping device having a basic body and gripping elements and more particularly, to a gripping device that can be made simply and is particularly suited for small objects.
Gripping devices of this general type are employed, for example, in robot technology and are described in numerous publications. An object to be gripped is mechanically clamped between two gripping elements and then, for example, held or transported to another position. Gripping elements for gripping microscopically small objects require greater fine-mechanical precision.
In addition to mechanical gripping elements, electromagnetic elements are often used. The object is held by magnetic forces which, by way of illustration, are produced with an electromagnetic coil. Although gripping devices of this type are able to operate without mechanical elements, they can only be used with magnetizable objects.
Mechanical gripping devices have gripping elements, which either must be movable (clamping jaws) or hinged (gripping fingers), and require a mechanical or electromechanical drive device. Such gripping devices are also subject to mechanical wear and tear.
Furthermore, because mechanical gripping elements require lubrication, they can, therefore, only be utilized to a limited degree under sterile or vacuum conditions.
IBM Technical Disclosure Bulletin (Vol. 25, No. 8, 1983, p. 4443), shows a gripping device which has a bimetal gripping arm. Upon suitable changes in temperature, this gripping arm bends in the direction of a stationary gripping arm and thereby clamps the object to be gripped between both gripping arms.
All the described gripping arms have limitations when it comes to gripping microscopic objects, as the fine-mechanical processes required for manufacturing the arms grow more and more complicated with increasing miniaturization and entail high costs.
An object of the present invention is to provide a simple gripping device that can be made without complicated fine-mechanical processes and is suited for gripping microscopically small objects (.mu.m range).
The aforesaid object has been achieved in accordance with the present invention by a gripping device in which the basic body consists of one or several semiconductor chips, and tongues are each composed of thin layers which are made with the aid of precipitation of vapor deposition processes. For changing the temperature, the tongues are equipped with layer-shaped heating elements applied onto or between the layers of the tongues.
It should be clearly understood that the gripping device can be fabricated in different sizes. As it does not require mechanical drive devices, the gripping device of the present invention is especially suited for miniaturization. Thus, it meets the demands of ever smaller handling systems, which are increasing with the growth of microtechnoloqy. Whereas the known gripping devices have limitations set by fine-mechanical manufacturing procedures, the gripping devices according to the present invention can be conducted in dimensions of several hundred micrometers with known microstructure technology methods.
The elements for heating the tongues are electric resistances and arranged between or on the layers of the tongues. The basic material for the basic body of the gripping device can be silicon wafers which have found wide application in microelectronics.
In order to be able to move the tongues at the lowest possible heat level, the tongues are made of a combination of materials having thermal expansion coefficients as different as possible. With the use of a silicon compound (e.g. silicon nitrite or silicon dioxide), microstructure methods have found application in the fabrication of particularly small-dimensioned gripping devices.
In order to be able to put the gripping elements in a predeterminable position and in order to avoid the ambient temperature from influencing the position of the gripping elements, one especially favorable arrangement attaches sensor elements to the tongues for detecting the momentary position and for controlling the position. The function of the sensor elements can be based on various physical effects. The use of piezoresistances is especially advantageous as the static piezoresistant effect is particularly pronounced with silicon and the position of the tongues can be determined immediately by measuring the pull and pressure force. Another advantage is that the piezoresistances can be easily fabricated with the aid of the conventional methods employed in microelectronics.
Heating and sensor signals can be linked in common control circuits, thereby permitting, by way of illustration, the tongues to be kept in the predeterminable positions by regulating the heat level. In this manner, the movement of the two corresponding tongues and also that of several gripping elements can be coordinated, thereby ensuring the handling cf large and complex objects. The design and effect of the individual gripping elements corresponds to the controllable position-changing element, which is described in the unpublished Patent Application DE 38 09 597.1. In order to achieve an especially high degree of miniaturized, the control circuits and the gripping devices can each be also be fabricated simultaneously.
Another advantageous feature of the present invention concerns the basic body which is composed of two silicon chips each carrying a tongue and joined via a spacer plate. The gripping device can be adjusted to the size of the object to be moved by the thickness of the spacer plate.
A presently preferred embodiment of the present invention is distinguished by having an especially simple build-up. Three tongues, which grasp the object to be moved by suitable steering, are attached to the basic body, which is made up of only one silicon chip.
The hereinafter described further features of the present invention are advantageously fabricated with known micromechanics and micro-electronics processes, and are compatible with standard IC processes. The individual components are structured with the aid of planar lithographic processes. The voltage levels common in microelectronics suffice for operating a gripping device.
The gripping device of the present invention is distinguished by having a high degree of miniaturization, high precision, great reliability and low costs. The extreme degree of miniaturization permits utilizing the gripping device for handling microscopic objects, e.g., in processing and analyzing objects in microtechnology or in microbiology. The gripping device is particularly suited for handling objects of this kind in closed systems in which mechanical operation must be avoided, by way of illustration, in ultra-high vacuum apparatuses.